The inefficient dissipation of heat is a crucial problem that limits the reliability and performance of electronic devices. In advanced electronic applications, everything is driven by size, weight, and power considerations. As devices have become progressively smaller, more powerful, and more complex, they dissipate much larger amounts of heat. There is higher heat dissipation per unit area. Heat is dissipated to the ambient environment. The heat created can erode the device if there is not a thermal interface material between the electronic device and cooling system. Thermal materials can be used to connect the microprocessor and a heat sink. Currently, thermal greases, elastomer-based composites, and solders are the most commonly used types of thermal interface materials used for enabling the efficient dissipation of heat. Epoxies, gels, and phase change materials can also be used as thermal interface materials.
In thermal greases, thermally conductive fillers are typically dispersed in silicone, sodium silicate, or a hydrocarbon oil to form a paste. As a filler, CNT, diamond powder, silver, and copper, have been employed in current thermal grease formulations. Polymer-matrix composite thermal interface materials (TIMs) typically involve the addition of thermally conductive particles into a polymer matrix. While epoxy, polyurethane, and polyvinyl chloride have been traditionally used as polymer matrices; silver, copper, and aluminum nitride particles have been used as conductive fillers. Alumina, silicon oxide, silicon nitride, silicon carbide, boron nitride, and aluminum nitride are also possible fillers. Epoxy composite TIMs containing novel types of fillers such as graphite, graphene, and CNTs can be used. Both thermal grease and polymer-matrix composite TIMs typically have thermal conductivity values ranging from 0.5 W/m·K to 7 W/m·K. A solder thermal interface material, which is a fusable metal alloy, melts at a rather low temperature. The molten solder can flow and spread itself thinly at the interface, thereby giving rise to a high level of thermal contact conductance. The thermal conductivity of solder TIMs generally ranges from 20 to 80 W/(m·K).
While solder thermal interface materials offer high thermal conductivities and low thermal interface resistances, their relatively high stiffness make them unsuitable for use across interfaces between materials with large differences in thermal expansion coefficient due to the risk of delamination and chip cracking. Elastomer-based TIMs are more compliant, but their relatively low thermal conductivity and poor thermal transport across the boundaries between the epoxy and the surrounding materials in the system pose a significant thermal barrier to high-power operation. Thermal greases are messy and difficult to apply and remove. In addition, the excess grease can leak into the surrounding and cause a short.
Better thermal interface materials are important for including but not limited to radars, laser systems, military electronics, and consumer electronics in order to prevent overheating of the device.